Hello everyone! I'm currently based at the Large Hadron Collider (LHC) at CERN in Switzerland, the facility where we probe the deepest questions about our universe(s) - where does mass come from, what is dark energy made of, how did everything begin (if there is actually a beginning in the conventional sense), where did all the missing antimatter go... Questions that we might finally answer with the LHC - the most powerful and most high-tech machine ever constructed!

The large circle is the LHC. Genève Aéroport is on the east.

Right now we have just publicly released the latest experimental results for proton collisions carried out from 2010-2011 at 7 terra-electron-volts (TeV) of energy. This is a really exciting time for us, because once we're sure everything is working smoothly, the LHC will be upgraded to its maximum capacity of 14 TeV, and that's where all the fantastic discoveries ought to happen.

An interesting collision event at the Compact Muon Solenoid (CMS) detector at the LHC.

How much more does our technology and science need to improve before we can test string theory?
Why is light the only wave that doesn't need a medium to propagate?
When we say light is made up of photons, can we break it down any further? I suppose since it's energy it doesn't count as matter.
Since light canges speed when entering different mediums, do we still say the spped of light is constant?
What is the actual temperarure in the middle of space? It's impossible to get to 0K, so what is the temperature in space when there's no stars nearby.

How much more does our technology and science need to improve before we can test string theory?

Actually, string theory also needs to improve itself to make more testable predictions! The main aspect of string theory currently testable by current technology like the LHC is that gravity is a lot stronger in higher dimensions, so the gravitational force that manifests itself in our space and time is really just 'leaking' out from those higher dimensions.

So if the LHC is able to detect the signature of higher dimensions in the collisions, then that would be a good place to start checking how well string theory works over there!

Why is light the only wave that doesn't need a medium to propagate?

No it isn't. The other force-carrier particles, like the gravitons, also don't need a medium to propagate.

From the wave point of view (actually, more of field here), electricity is able to induce magnetism and vice versa (that's how electricity is generated at a powerplant anyway), so even in vacuum, a fluctuation in the electric field is able to disturb the magnetic field, so they take turns to transmit the energy along, not surprisingly at the speed of light, as Maxwell calculated.

When we say light is made up of photons, can we break it down any further? I suppose since it's energy it doesn't count as matter.

OK so now we're looking at it from the particle point of view. Einstein and friends established like 100 years ago that light comes in fixed units of energy, which is why they behave as photons in the first place. So once you reach a single unit, you can't break it down any further, just like you can't pay for something that costs half a cent.

Incidentally, energy and mass are actually different aspects of the same thing (to wit, E=mc^2), but in this case the formula is E=pc, because photons are massless.

Since light canges speed when entering different mediums, do we still say the spped of light is constant?

Speed of light (c) is constant in vacuum when there are no forces acting. This is a consequence of Einstein's special relativity, which states that the laws of physics must be the same for all observers in no-forces-acting frames. So all observers will measure the same speed of light.

What is the actual temperarure in the middle of space? It's impossible to get to 0K, so what is the temperature in space when there's no stars nearby.

That would be about 3K.

In comparison, the superconducting magnets used at the LHC is about 1.9K.

Has CERN made mini black holes yet? If so, how stable are they. Also, do you think that these mini black holes have the potential to destroy our planet or is this a fear blown out of proportion?

Nope, CERN hasn't produced any mini black holes yet. Sorry to disappoint any fans out there.

At the moment, LHC is still running at half the maximum energy so that we can double check our current understanding of the existing physics. We're only expecting to discover exciting new physics when the LHC reaches its maximum energy of 14 TeV.

I do not think that any mini black holes the LHC may produce can destroy the Earth because of 2 things that we already know about black holes.

1. Black holes have a limited radius where they become effective. You could think of it as like a vacuum cleaner vacuuming near a curtain - as long as you don't go too close, the curtain doesn't get sucked in.

2. Black holes should dissipate eventually by giving off Hawking radiation. (Apart from a puddle of water, I can't think of any better example though. ) Actually NASA is also studying this effect, but they are focusing on the massive black holes out there in space.

So, the black hole specialists estimate that the mini black holes should evaporate within 1/10^27 seconds, and what we're really looking for are their decay products which are supposedly particle jets spraying in 10 directions.
If we see that at the LHC detectors, I believe CERN would phone all the major news companies immediately.

So if a black hole decays, does it spit back all the matter that it ate all at once?

Hmm this is a tricky question. First of all, massive black holes decay slower than tiny ones. You could think of it like baking a pie - a large pie in the open takes a longer time to cool off than a smaller pie. Since the mini black holes we hope to see at CERN are really small, they should decay in a split-second.

Secondly, since mass and energy are more or less the same thing (E=mc^2 again) then yes, the total energy content that goes in comes out eventually, though not necessarily in the same form, kind of like how the food that goes in through the mouth and comes out through the rear-end doesn't stay in the same form.

HOWEVER, while it's actually possible to deduce from the shit what a person ate, anything that fall into a blackhole is utterly and irretrievably destroyed. This means that it's not possible, even in theory, to work out from the Hawking radiation what originally went in. This results in what is known as the black hole information paradox, which is a kind of cosmic shredder with 100% perfection. This is still an unsolved problem in cosmology.

For readers who don't know, when the Universe began, matter and antimatter should have formed in equal amounts, because antimatter is supposed to be like the exact complement to matter, sort of like Yin and Yang; they differ only in their electric charge - an electron is -ve but a positron is +ve. But the thing is that virtually everything in the Universe today is made of matter, from our solar system to far-flung galaxies. Where then, have all the antimatter we reasoned should exist disappeared to?

The answer is no, we haven't found out. This antimatter mystery could be due to some symmetry breaking or violation, so the LHCb detector (run by a different group from CMS) aims to spot these rare events in the proton collisions. Another group here known as ATRAP is studying lab-created antimatter directly by capturing positrons with anti-protons to form anti-hydrogen - their latest achievement was to store these anti-hydrogen atoms for 15 minutes (see article below). I think we can safely expect greater technological and scientific breakthroughs at CERN in the coming years.

And of course, NASA also has its own project for this. The Alpha-Magnetic Spectrometer detector (AMS, assembled at CERN ) was recently installed on the International Space Station to look out for antimatter coming in from high-energy cosmic rays from outer space. If they actually find anti-helium or some other heavier anti-atoms, that should be the biggest science news of the decade.